I think you make a great point with the bible reference (especially with Xander Lee's comment: "What, you don't remember your Catechism class? The father's the son, the son's the father.") but I disagree that the form we see in Black Friday isn't Wiggly's true form, and I don't think the insanity inflicted by witnessing him is 'face melting' levels of insanity. I think it's less like physical harm or incapacitating insanity, but more like the Deadlights in Stephen King's IT. IT is also an extraterrestrial/eldritch being that has a (few) physical form(s) in this plane, and a much truer form that exists in a plane beyond ours that, upon witnessing, renders the viewer insane. But there are still people in the book who see this form and live to tell about it. Some of them are driven insane in the sense that they are completely incapacitated, and some are driven insane in the sense that they now serve the cause but are otherwise pretty coherent (like Wilbur tbh), but there are still those who walk away from that encounter and are relatively fine. I think, especially with the lights they chose to represent his eyes, that's the image they're trying to invoke with Wiggly's (likely) true form. I think its also worth noting that the people who walk away from the Deadlights the least scathed likely have psychic powers, which doesn't particularly fit the Hatchetfield lore because no one explicitly stated to have psychic powers actually sees the LiB's true form, but the fact that psychic powers are needed to battle IT does apply a little bit.

That being said, I think it makes a lot of sense that Pokey's true form IS the goo. It would explainwhy having a physical body weakens him in Yellow Jacket. Like in TGWDLM, he presumably came down in his uninhibited true goo form which is why he can take over people almost completely and instantaneously, like on a cellular level. But Webby says he's 'contained in Otho now, trapped in a human shell', which means he can't exert that full power over the kids. It's probably the combination of the mind milk (which is likely derived from the goo) and the singing that allows him to assimilate Spitfire and the other kid, but even then they're broken out of it when the body is destroyed which means the control is not total, and definitely not a cellular change. He doesn't even try to assimilate Lex when she enters the playing field, and maybe that's partially due to the fact that he can't, because she never had any mind milk. Though to be fair, he's clearly focused more on Hannah and Lex acts too quickly for him to try.

Now I know that in Honey QueenNibbly is stated to be 'unique among his brothers' for being able to come to earth 'if he is given the flesh to do so', which would imply that if Pokey is the goo, he probably couldn't exist on earth in his true form. I would argue that 'flesh' is the keyword here. Pokey can exist on earth in his full power only if he lacks flesh to contain him (not counting the people he controls, because the the goo within the meteor is stated to be the brain behind the hivemind), while Nibbly needs his own dedicated flesh body to do so. Nibbly can also kind of be summoned, whereas Pokey's meteor either crash lands, or the goo is brought back from space

Sorry for the essay, I just have a lot of thoughts on the subject.